1. Field of the Invention:
The present invention relates to a method for correction of a defect in a circuit pattern having a protective film such as an X-ray exposure mask used to form an extremely fine pattern of a magnetic bubble device, a semiconductor integrated circuit or the like.
2. Description of the Prior Art:
With the recent trend toward enhancing the integration density of semiconductor integrated circuit elements and so forth, an X-ray exposure process is generally applied as a means for forming a fine pattern. According to this process, first a heavy metal pattern is formed on a thin backing member to serve as an X-ray absorber, subsequently an element such as a silicon wafer is coated with an X-ray sensitive resist, which is then exposed to X-rays. Since the X-ray wavelength is far shorter than that of light, a high precision is attainable in forming a pattern with another advantage of satisfactory adaptability for mass production.
FIGS. 1 and 2 illustrate exemplary structures of such X-ray exposure mask (hereinafter referred to simply as X-ray mask). In the example of FIG. 1, a thin film 202 of boron nitride BN is formed on a mask frame 201 composed of a silicon wafer. A central portion of the mask frame 201 composed of silicon wafer is removed by etching so that a window 201a is formed for achieving ready permeation of X-rays. After a plating electrode 203, permeable to X-rays, is formed thereon, a heavy metal pattern 205 is formed by plating and then is coated with a protective film 204.
In another example illustrated in FIG. 2, a thin film 302 of silicon nitride or the like is formed on a mask frame 201 composed of a silicon substrate and, after a heavy metal is deposited thereon, its pattern 205 is formed by dry etching and then is coated with a protective film 204.
In the patterns 205 - 205 and 205 mentioned, defects are caused by some extraneous substances or the like. FIG. 3 illustrates examples of such defects, in which (A) represents a black spot defect where the pattern is deposited in excess, and (B) represents a white spot defect where the pattern is dropped out.
If any of such defective masks is transferred, it directly brings about a defect in the resultant pattern of an LSI, and therefore the defect needs to be corrected in the stage of forming a mask.
However, the X-ray mask pattern is as fine as 0.5 .mu.m or less and still has a height of 0.5 .mu.m or more for absorbing X-rays.
It has been customary heretofore to employ a laser for correction of any black spot defect in a photo mask, but complete correction of such fine pattern is technically difficult due to the thermal process and the limitation in the laser beam convergence. In an attempt to solve the problems mentioned, there is currently carried out an improved method which performs desired correction by the use of a submicron focused ion beam, as disclosed in Japanese Patent Laid-open No. 58 (1983)-56332 (U.S. Pat. No. 4,503,329) "Method and Apparatus for Correcting Defect in Mask".
However, while the above method is effective for correction of black spot defects it is not directly applicable to the correction of white spot defects.
With regard to white spot defects, a method based on the deposition of a heavy metal is effective as described in Minafuji et al. "Characteristics of Tungsten Film by Focused Ion Beam CVD" (Drafts for Joint Lecture in 33rd Meeting of Applied Physics Society, p. 339). A particularly remarkable effect is supposed to be achieved by the method which locally decomposes and separates a metal compound by the use of an ion beam.
The above methods, however, still include a problem relative to the contamination of a vacuum receptacle, an ion source, an ion-beam optical system and so forth with organic metal gas and are therefore not satisfactory for practical use. Furthermore, the gases employed in the above are mostly dangerous ones with respect to the properties of ignition, poison and corrosion. As a result, measures for maintaining safety are required which eventually cause a higher production cost for the apparatus.
As for other related art, there are additional techniques for defect correction. One is described in Japanese Patent Laid-open No. 58 (1983)-111317. This document disloses a photo mask correcting method characterized by electroless-plating of the photo mask, thereby forming a metal film on its defective portion such as a pin hole, to be non-transparent. Another technique is disclosed in Japanese Patent Laid-open No. 60 (1985)-234320. This document discloses an improvement of correcting a defect in a photo mask having a dropout in a portion of a pattern, characterized by first executing an electrolytic or electroless-plating step while converging and irradiating a laser beam of a wavelength shorter than 1.3 .mu.m, and increasing the plating speed in the portion being irradiated with the laser beam, thereby selectively depositing a metal and correcting the dropout.